A control approach is presented for model-unknow multi-input multi-output(MIMO) pure feedback systems. During every step of back-stepping, the prescribed performance control theory is adopted to construct the nonlinear proportional back-stepping controller. Based on comprehensive consideration of the the unknown model, state constraints, input saturations and prescribed performance, the proposed scheme has satisfactory anti-disturbance ability, adaption and robustness without introducing any approximation structures and adaptive control. The design procedure and structure of the proposed scheme is very simple. Finally, the stability of the close-loop system is proved based on the Lyapunov stability theorem. The simulation results show the feasibility and effectiveness of the proposed control schemes.